Due to their excellent circular polarization over a wide angle, resonant quadrifilar helix antennas (QHA) are widely used in many applications. This antenna has particularly found application in satellite to ground communications, including aircraft mobile communication systems and military applications. Examples of such products include satellite navigation systems, satellite tracking and locator systems (e.g., GPS), and communications systems (e.g., NAVSTAR) that rely on satellites to relay the communications signals from one station to another.
The fractional-turn resonant quadrifilar helix produces a cardioids-shaped radiation pattern. To shape the antenna patterns prior art used multi-turn elements that are longer than one wave length.
Conventional designs could accomplish hemispherical non shaped simple patterns. However, there is no conventional design having a shaped pattern antenna using arms that are shorter than one wavelength.
Example embodiments of this disclosure provide a cosecant-squared-shaped pattern that is realized using a fractional-turn quadrifilar helix with an arm length that is less than one wavelength.
Additionally, most satellite communication and other systems require dual-band operation. One way in which a dual band antenna can be made is to stack two single-band quadrifilar helix antennas end-to-end, so that they form a single, common axis cylinder. Clearly, a big disadvantage of this solution is that such an antenna is much longer than would otherwise be desired for many applications.
Prior art techniques for providing dual-band (or Multi-Band) performance is described in U.S. Pat. No. 6,421,028. The '028 patent solves the problem of a dual frequency antenna but does not solve the shaped pattern issue.
Therefore, there is a critical need for an antenna that operates over multiple frequencies and that is in a small enough package such that it is suitable for portable applications. Example embodiments provide a technique capable of providing a shaped pattern antenna that is realized using a fractional-turn quadrifilar helix with an arm length that is less than one wavelength.